Panel with longitudinal mirrors for a solar power plant

ABSTRACT

A receiver for a solar power plant with mirrors ( 7 ) and horizontal longitudinal receivers ( 1 ) includes a rotating shaft and axis of symmetry which ( 14 ) are parallel to a longitudinal axis of the radiation receiver. The receiver is formed by a balanced expansion and pressure collector, the tubes ( 19 ) of which are grouped in a separate central bundle ( 20 ) and adjacent bundles ( 21  and  22 ), thermally insulated from one another longitudinally. Heat transfer fluid circulates first through both adjacent bundles in parallel, to then be injected into the central bundle, where the radiation intensity received is greater because of receiving the radiation from the array of mirrors focused on the midline of the active face ( 2 ) of the receiver, each bundle of tubes being able to be covered by a separate ( 60, 61, 62 ) transparent window ( 28 ).

FIELD OF THE ART

The invention is encompassed within the field of solar energy powerplants requiring concentration of source radiation, which in this caseis reflected by a series of longitudinal, horizontal or slightlyinclined mirrors which can be oriented by rotating about theirlongitudinal axis of symmetry; the reflected radiation being focused onan also longitudinal receiver, with its long axis being horizontal orslightly inclined, and with a certain transverse inclination.

The receiver is intended for transferring a substantial part of theenergy produced by the photons of the solar radiation striking thereceiver to a fluid. To that end the receiver will have an activesurface or face with suitable optical and thermal properties, consistingof having high absorptivity to solar radiation and a low typicalemissivity. That active face should be thermally connected to a group ofparallel tubes the axes of which are in turn parallel to thelongitudinal mirrors. A heat transfer fluid transporting the absorbedsolar heat to a useful purpose, which will be a thermal application, andparticularly a thermodynamic cycle, which will be applied to ahigh-temperature thermal solar power plant, usually intended forgenerating electricity, circulates through the inside of the tubes. Theactual outer surface of the tubes where the radiation strikes can be theactive face of the receiver, although other configurations are possible.In any case, the geometric and thermal structure of the receiver is akey factor for achieving the objective sought, requiring a high captureof heat by said fluid, called heat transfer fluid, in order for thefluid to reach the temperatures required by the thermal application.

BACKGROUND OF THE INVENTION

This invention directly relates to two other inventions, the firstinventor of which is the first inventor of this application. The firstis a specific background document concerning the receiver and is Spanishpatent ES 2 321 576 B2, granted on 13 Oct. 2009 (Official IntellectualProperty Bulletin (Boletin Oficial de la Propiedad Industrial)) andfiled on 31 Dec. 2008, with no. P200803767. A balanced expansion andpressure receiver, ideal for receiving radiation on a facade typesurface, although having a geometry adaptable to the field of mirrorsfrom which it receives the radiation, is presented in this invention.

The second invention is another application from the same holder and thesame inventors as this one, entitled SOLAR RADIATION CONCENTRATINGDEVICE, WITH LONGITUDINAL MIRRORS AND RECEIVER, filed in the SPTO withno. P201000644. In it the position, size and curvature requirements formirrors are established, as well as position and size of the receiver,although without giving any requirement as to the content of the lattergiven that said solar radiation concentrating device can be applied forany purpose. The receiver of the solar thermal power plant establishedin the present invention can also operate with radiation concentrated byany longitudinal device. Two background documents disclosing fields ofmirrors and longitudinal receivers which are very representative of thestate of the art as they are very close in time are mentioned below.

International application WO 2009/029277 A2 proposes a conventionalFresnel configuration with multi-tube receiver and many configurationvariants, although without numerical assembly requirements, and withvery generic claims; using planar and concave mirrors in FIGS. 3 and 4,without further specification, and concave mirrors in FIG. 12, alsorelating to the configuration of hydraulic circuits in the multi-tubereceiver, although without grouping them in bundles with a differentfunction because of receiving different levels of intensity, does nottake into account the natural aperture of sunlight. WO 2009/023063A2relates to a receiver inclined with respect to the ground, with anasymmetric structure to favour collecting radiation, but it does notapproach grouping in bundles for a progressive heating of the heattransfer fluid without the unnecessary generation of entropy.

TECHNICAL PROBLEM TO SOLVE

A fundamental physical fact is that solar radiation is not perfectlycollimated, but comes from the Sun, which has an optical aperture fromEarth of 32′ (sexagesimal minutes), its intensity being virtuallyuniform in the entire Sun, as corresponding to radiation emitted in aperfectly diffused manner from a spherical surface. This aperture meansthat the radiation striking a point of the Earth's surface is not simplymade up of a ray from the Sun, but is a cone of rays the conical angleof which is precisely the aforementioned 32′. Therefore, and dependingon the light reflection principle, a single ray does not emerge from thepoint in question, but a group of rays, or beam, with an apertureexactly equal to that of the striking beam, i.e., 32′. This aperture isequivalent to 0.0093 radians (or 1/107.5 radians), meaning that when thebeam covers relatively long distances, the surface of its perpendicularsection becomes increasingly larger, which produces a low intensity inthe receiver absorbing solar radiation.

Moreover, when the radiations reflected by several mirrors aresuperimposed on the active face of the receiver, for increasing theintensity of the radiation, which is expressed in W/m² in the SI system,the surface distribution of the intensity shows important variationsbecause it is greater in the central area, towards which the reflectedlight beams are focused, and is less towards the periphery of the activeface of the receiver, where the intensity decreases like the sides of abell curve.

A low value of radiation received prevents the heat transfer fluidcirculating through the tubes of the receiver absorbing radiation fromreaching high temperatures because not even the active face reachesthem. In fact, the maximum absolute temperature which the active face ofa receiver like the one proposed herein can reach depends on thefollowing factors:

A=absorptivity of the active face to solar radiation.

E=emissivity of the active face (depending to a certain extent on thetemperature of the active face).

I=intensity (W/m²) of the radiation received

The maximum absolute temperature T in K (Kelvin) which can be reachedwith those conditions is

T=(A·I·10⁸/5.67·E)^(1/4)

The above equation assumes that there is no heat transfer mechanismother than radiation on the active face of the receiver, implying thatthe heat capturing efficiency by the fluid would be nil. In reality, alarge part of the heat will be transferred to the fluid, and there willfurther be convection and conduction losses, so the actual T of areceiver will always be below the aforementioned temperature, which hasthe advantage of demonstrating the dependence on temperature withrespect to intensity, I. In qualitative terms it can be said that incomplete thermal balance of a receiver, the temperature of its activeface and the temperature of the fluid will be greater with higherintensities if other intervening factors remain constant.

On the other hand, if the different areas of the active face receiving adifferent intensity, they exchange said energy, the heat from the hotterparts passing to the less hot parts, the temperature becomes uniform,entropy increases and exergy decreases, negatively affecting the energyand exergy efficiencies of the purpose of the receiver, which is to heatthe heat transfer fluid to a high temperature and with a sufficient flowrate.

Similarly, if two fluid streams at different temperatures are mixed, atemperature compensation averaged with the weights of the heat transfercapabilities takes place, entropy increases and exergy decreases. Thismeans that mixing at different temperatures by conduction or at a flowrate level is detrimental to the goals of a thermal application.

Therefore, the technical problem this invention solves is usingradiation reflected by a longitudinal mirror concentrator device suchthat high energy and exergy efficiency values are achieved despite thedifferences in intensity of the radiation received in the central partand in the peripheral part of the active face of the receiver.

The costs of producing thermal energy at a high temperature from solarradiation can be significantly reduced with a radiation receiver encasedin a receptacle with special features to be a balanced expansion andpressure receptacle, and all as a result of obtaining a high enoughconcentration of solar radiation on the receiver, with a very simple,easy to maintain and clean field of mirrors. The receiver also has theadvantages of not needing rotary joints in the tubes absorbingradiation, or welds between the tubes and their glass covers, like thoseneeded in parabolic trough collectors currently on the market, which arethe conventional configuration but have weak points like thoseindicated.

DESCRIPTION OF THE INVENTION

The invention consists of configuring the solar thermal power plant withthe following elements:

-   -   a longitudinal solar radiation receiver formed by bundles of        parallel tubes contained inside a balanced expansion and        pressure receptacle-collector that is much longer than it is        wide, the group of outer surfaces of the tubes where the        radiation strikes being the active face, or the active face or        surface being where the radiation strikes, thermally connected        to the surface of the tubes, and said receiver being able to be        formed by a consecutive group of longitudinal receptacles,        preferably balanced expansion and pressure receptacles,        successively interconnected for the passage of the heat transfer        fluid, said tubes having a horizontal longitudinal trajectory or        with the inclination given to the mirrors; the mentioned tubes        being grouped transversally in at least three longitudinal        bundles, there being a central bundle of longitudinal tubes, and        at least two adjacent bundles, one on each side of the central        bundle, these bundles being able to go in the same receptacle or        in adjacent receptacles, but in any case their heat transfer        fluid streams not mixing when they pass through the receiver,        the central bundle and adjacent bundles having longitudinal        thermal insulation between them separating them;    -   the percentage distribution of the total active surface of the        receiver between the central bundle and the adjacent bundle of        tubes being a value selected from the central bundle occupying        99% of the active surface, and the adjacent bundles occupying        the rest; and the central bundle occupying 20%, and the adjacent        bundles occupying the rest; giving 50% of the active surface        occupied by the central bundle as a distribution reference        value, and the adjacent bundles each occupying 25% of the total        active surface of the receiver on either side;    -   and said receiver being supported in height by pillars or        structural frames, generally transversely braced, with an        aboveground height in accordance with the reflection of the        radiation reflected by the mirrors;    -   and an array of longitudinal mirrors, the longitudinal axis of        symmetry of each mirror being parallel to the longitudinal axis        of the receiver, forming a direct solar radiation concentrating        device, and the requirements of which do not from part of this        invention, although these devices are essential for the        operation of the power plant.

In a solar power plant there can be a plurality of these receiver-mirrorarrays parallel to one another. They could have the same or differentlengths according to the relief of the terrain, and these arrays couldbe hydraulically connected to one another through the heat transferfluid circuit, either in series or in parallel, depending on thermalhydraulic design which is to be followed in each power plant, althoughthe reference assembly is a parallel hydraulic connection, eachcollector taking the fluid from the pipe coming from the thermalapplication with the relatively cold fluid, and sending the fluid to thereturn pipe to said application once it is heated.

A fundamental issue of the invention is that the central bundles of eachreceiver receive the most concentrated radiation while the adjacentbundles receive the least concentrated peripheral radiation since mirrorfocus requirements establish that the normal to each mirror at thecentral point of its perpendicular section at all times is the bisectorof the angle formed by the sun ray striking that point and the linejoining said point with the central point of the perpendicular sectionof the receiver, that perpendicular section corresponding to the samesection, transverse to the longitudinal axis, as that of theperpendicular section of the mirror. All this is expressed in theworking plane.

The invention can preferably be made in two geographic configurations:according to the local meridian, or North-South, and according to thelocal latitude, or East-West.

A dual assembly with two symmetrical receiver assemblies opposite oneanother, with the respective active faces pointing to the correspondingfield of mirrors is used as a reference configuration in botharrangements, according to the meridian or according to the latitude. Inthat basic though not the only assembly of the invention, the receiversserve as outflow and return means in the heat transfer fluid hydrauliccircuit, said fluid being heated by the radiation reflected by the twoparallel fields of mirrors, one of them reflecting at that time on thefirst receiver, and the other field on the other side of the receiversreflecting on the second receiver. The difference that may exist betweenone field of mirrors and the other due to the position of the Sun atthat time will thus be compensated. However, variants which do notfollow that concept and which only use one receiver with itscorresponding field of mirrors on only one side, i.e., on the side ofits active face, are contemplated.

In the dual or reference assembly with two receivers opposite oneanother by their rear faces, the heat transfer fluid first flows throughthe adjacent bundles of one of the receivers, specifically the onereceiving less solar intensity of the two at that time, then passes tothe adjacent bundles of the receiver of the other face, and afterrunning through it longitudinally, the pooled heat transfer fluid fromboth bundles passes to the central bundle of the first receiver, flowingalong it to then pass to the central bundle of the second receiver,whereby ending the heat transfer fluid heating process, the heatingprocess thus being optimised for achieving the highest possibletemperature with the available solar conditions, using the area of thehighest concentration of radiation for the final heating.

In the arrangement with a single receiver and a single array of mirrors,the heat transfer fluid first circulates in parallel through theadjacent bundles in one direction, and all the fluid returns through thecentral bundle of the same receiver in the opposite direction, for whichpurpose it is injected into the central bundle from the adjacentbundles.

A fluid circulation variant in dual assemblies is that the fluid doesnot pass from one receiver to another in double outflow and return, butcirculates as in the case of a single receiver, through both receiversindependently, the heat transfer fluid first circulating in parallelthrough the adjacent bundles in one direction, and all the fluidreturning through the central bundle in the opposite direction, forwhich purpose it is injected into the central bundle from the adjacentbundles.

The corresponding group of controllable pumps and valves is arrangedexternal to the receiver itself but essential for the operation of theinvention for forcing the heat transfer fluid to follow these movementsthrough the described circuits.

The width of the active surface of the receiver, referred to as R, isdetermined depending on the natural aperture of solar radiation of0.0093 radians, and the straight line distance from the central point ofthe final mirror of the field to the central point of the receiver, and1% of said distance corresponds specifically as a reference value forsaid width, values greater than 5% or less than 0.1% being able to bechosen without compromising the principle of the invention, although thepower plant efficiencies are different from those obtainable with thereference value, which always produces efficiencies close to optimalefficiency.

In its basic version, the receiver is built with a trapezoidalperpendicular section, its outer transparent surface or transparentwindow having a greater width than the width of the active face in whichthe radiation is absorbed and which is connected to or coincides withthe central and adjacent bundles of tubes inside which the heat transferfluid circulates. These bundles of tubes are kept in their positions bythe bent tubes traversing the receptacle of the receiver, which issuspended from the securing columns or frames through the attachmentpart. The receptacle has open side walls at the end of which there arelocated the gaskets in which the transparent window is anchored. Saidside walls have an opening at the lower end parallel to the line joiningthat end of the active face to the closest point of the mirror closestto the receiver, the opening at the upper end being parallel to the linejoining that end of the active face to the point furthest from themirror furthest from the receiver. All this is expressed in the workingplane.

The central and adjacent bundles have a longitudinal thermal insulationbetween one another separating them for the purpose of minimising theloss of high temperature heat involved in the heat transfer from thecentral bundle to the adjacent bundles, which would be in detriment tothe good exergetic balance of the system.

A structural variant consists of arranging the bundles of longitudinaltubes of the receiver obliquely to one another, the entire angle throughwhich the radiation arrives being covered by the active surface of thetubes as a result of the covering provided by the bundles, there evenbeing a small area in which a shadow of the end of one bundle is cast onthe contiguous bundle, with an extension no greater than half the radiusof the tube in the shadow without there being physical contact betweenthe ends of both bundles, and thermal insulation parts furtherpreventing the passage of convection currents being able to beinterposed between them without physical contact with both at the sametime if there is filling gas in the receptacle of the receiver.

The width of the active face of the receiver is the distance between theend points of the adjacent bundles on each side. The group of bundlesdoes not have to be symmetrical with respect to the central point,although symmetry may have constructive advantages. The most extreme rayof radiation reflected up strikes the upper end point of the activeface, and the most extreme ray of radiation reflected down strikes thelower end point.

With this trapezoidal arrangement, the intensity of the radiationtraversing the transparent window, which is never perfectly transparent,is less than the intensity received on the active face. This reduces thethermal load due to the radiation deposited on the transparent surface,which is important because it is not a cooled element.

As an assembly variant, the transparent surface can be made of partialwindows, each covering one bundle, and may not be planar butdome-shaped, either with a semicircular perpendicular section, or with apointed perpendicular section, the intermediate supports of the partialwindows coinciding with the thermal insulations separating the centralbundle from the two adjacent bundles.

With respect to the height for locating the receiver, it is deduced bythe details that the angle of vision of the central point of thereceiver from the central point of the furthest mirror is selected in arange of values between 10° and 80°, with an optimal value of 45°,measured on the horizontal of the location; and the inclination of theactive face of the receiver being determined in that the segment markingsaid surface in the working plane is perpendicular to the bisector ofthe field, said bisector being that of the angle formed by the linesgoing, respectively, from the central point of the active face of thereceiver to the central point of the mirror closest to the receiver andto the central point of the furthest mirror.

DESCRIPTION OF THE DRAWINGS

The drawings are not to scale since the width of the receiver andmirrors will be will be considerably less than their length and alsomuch less than the height at which the receiver is supported.

FIG. 1 shows a perpendicular section diagram of the solar power plantcorresponding both to an assembly according to the meridian and to adual assembly according to the latitude, with an array of mirrors to thenorth and another to the south of the respective collectors in thiscase.

FIG. 2 shows the three-dimensional diagram of a receiver-mirror assemblyin the assembly according to the latitude, with an arrangement to thenorth of the latitude in the northern hemisphere.

FIG. 3 shows a cross-section view of the solar receiver in the geometryof the invention, where the four central tubes form the central bundle,and the two end tubes form the corresponding adjacent bundles on eachside.

FIG. 4 shows a cross-section view of the solar receiver similar to thepreceding view but with the bundles of adjacent tubes inclined withrespect to the main bundle, which allows better thermal separationbetween them and not losing radiation collecting capacity due to theinsulation.

FIG. 5 shows the profile of the intensity received on the active face ofthe receiver with a maximum in the centre corresponding to the centralpoint of the cross-section of the receiver.

FIG. 6 shows the circulation diagram of the heat transfer fluid in thebasic assembly of two receivers geometrically assembled in parallel andhydraulically assembled in series with the active faces opposite oneanother facing outwards.

FIG. 7 shows the circulation diagram of the heat transfer fluid in theassembly of one receiver, or two parallel receivers opposite one anotherbut operating independently in hydraulic operating conditions.

FIGS. 8 and 9 relating to the type of collector referred to as abalanced expansion and pressure collector, which is one of the genericsystem models which could be used as a basis for the application of theinvention, are added as a depictive complement. Therefore, the figuresare from document ES 2 321 57682 cited above as background, and ismerely illustrative.

FIG. 8 shows the longitudinal diagram of a balanced expansion andpressure collector in which the circulation of the heat transfer fluidgoes from left to right. The assembly is actually much longer in thelongitudinal direction from left to right than from top to bottom in thedrawing.

FIG. 9 shows a cross-section view of the solar receiver in the variantof separating the bundles of tubes in adjacent receptacles, although thephysical separation between them, including the insulation, is much lessthan the width of each bundle and is not to scale in the drawing. Thewindows of each bundle are pointed or semicircular in theirperpendicular section.

EMBODIMENTS OF THE INVENTION

The relevant elements of the drawings of the invention are listed belowin order to facilitate understanding of the drawings and embodiments ofsaid invention:

1. Receiver for concentrated solar radiation (6).

2. Active surface or face of the receiver (1).

3. Central point of the segment representing the active face (2) of thereceiver (1), in its perpendicular cross-section.

4. Direct solar radiation.

5. Longitudinal mirror reflecting the original solar radiation on thereceiver (1), and which is closest to the receiver.

6. Solar radiation reflected by the mirrors (7).

7. Generic mirror which is struck by solar radiation (4) which isreflected as concentrated radiation (6) on the receiver (1). There is aplurality of parallel mirrors reflecting the radiation on the samereceiver (1). There can be more than one field of mirrors in a powerplant, each focused on a receiver or lineal series of receivers.

8. High columns or pillars maintaining the solar receiver (1) and allits internal elements at their height and in position.

9. Low pillars maintaining the axes of the mirrors generically depictedas (7) at their height and in position.

10. Y-axis of the working plane for a specific field of mirrors which isthe vertical axis passing through the central point (3) of the activeface (2) of the receiver (1) receiving the radiation reflected (6) bythe array of mirrors (7).

11. X-axis of the working plane which is the horizontal line passingthrough the central point of the mirror (5) closest to the receiver (1),and is therefore perpendicular the y-axis (10).

12. Point of origin which is the intersection between axes (10) and(11).

13. Vertical axis of symmetry in dual assemblies different from axis(10) determining the reference coordinate system in each case.

14. Longitudinal axis of a generic mirror (7) about which it rotates foracquiring the transverse inclination necessary in the working plane.

15. Rotating junction of the pillar (9) with the rotating shaft (14) ofthe generic mirror (7) as the result of a bearing.

16. Securing part for firmly securing the receiver (1) to the column (8)in the upper part, allowing the receiver to expand vertically,maintaining its angle of inclination. It can have variousconfigurations.

17. Transverse bracing cables for bracing the pillars or columns (8).

18. Upper crosspiece for stiffening the receivers in double or dualassemblies.

19. Group of longitudinal tubes grouped in bundles inside the receiver(1) of solar radiation (6), inside which the heat transfer fluidcirculates, carrying most of the heat deposited by the radiation on theactive surface (2) of the receiver (1).

20. Central bundle of tubes (19).

21. Adjacent bundle of tubes on one side of the central bundle.

22. Adjacent bundle of tubes on the other side of the central bundle.

23. Thermal insulation longitudinally interposed between the centralbundle (20) and the adjacent bundles (21), (22).

24. Main body of the receptacle of the receiver (1).

25. Securing element for securing the receptacle (24) attached to thepart (16) in the support columns or pillars of the receiver (1).

26. Upper end point of the active surface (2).

27. Lower end point of the active surface (2).

28. Transparent window of the receiver (1).

29. Upper end ray of those reflected by the mirrors (7) pointed towardsthe receiver (1), striking point (26).

30. Lower end ray of those reflected by the mirrors (7) pointed towardsthe receiver (1), striking point (27).

31. Securing gaskets for securing the transparent surface (28) to themain body (24) of the receiver (1).

32. Mirror furthest from the receiver (1).

33. Ground and foundation.

34. Central point of the mirror (5) closest to the receiver.

35. Central point of the mirror (32) furthest from the receiver.

36. Transverse width of the active face (2) of the receiver (1) wherethe concentrated radiation (6) strikes.

37. Transverse width of the active face (2) of the receiver (1)corresponding to the central bundle (20).

38. Transverse width of the active face (2) of the receivercorresponding to the adjacent bundle (21).

39. Transverse width of the active face (2) of the receivercorresponding to the adjacent bundle (22).

40. Transverse profile of the intensity (W/m²) of the radiation strikingthe active face (2) of the receiver (1).

41. Separation by means of thermal insulation between the active face ofthe adjacent bundle (21) and the central bundle (20). It can be madewith various configurations.

42. Separation by means of thermal insulation between the active face ofthe adjacent bundle (22) and the central bundle (20). It can be madewith various configurations.

43. First receiver in a dual assembly corresponding to the one receivingless radiation intensity.

44. Second receiver in a dual assembly.

45. Hydraulic connectors from the pipe of relatively cold fluid comingfrom the thermal application entering the adjacent bundles of the firstreceiver (43).

46. Adjacent bundles of the first receiver (43).

47. Central bundle of the first receiver (43).

48. Hydraulic connectors from the adjacent bundles of the first receiver(43) to those of the second receiver (44).

49. Adjacent bundles of the second receiver (44).

50. Hydraulic connectors from the adjacent bundles of the secondreceiver (44) to the main bundle (47) of the first receiver (43).

51. Hydraulic connector connecting the central bundle (47) of the firstreceiver (43) to that of the second one (44).

52. Central bundle of the second receiver (44).

53. Hydraulic connector connected to the pipe of heated fluid going tothe thermal application from the central bundle (52) of the secondreceiver (44).

54. Receiver assembled in single or dual arrangement but with anindependent heat transfer fluid circuit.

55. Hydraulic connectors from the pipe of relatively cold fluid comingfrom the thermal application entering the adjacent bundles of theinsulated receiver (54).

56. Adjacent bundles of the insulated receiver (54).

57. Hydraulic connectors from the adjacent bundles of the insulatedreceiver (54) to the main bundle of said receiver.

58. Central bundle of the insulated receiver (54).

59. Hydraulic connector connected to the pipe of heated fluid going tothe thermal application from the central bundle (58) of the insulatedreceiver (54).

60. Transparent pointed window of the central bundle (20).

61. Transparent pointed window of the adjacent bundle (21).

62. Transparent pointed window of the adjacent bundle (22).

63. Bent connection tubes connecting the inner tubes (19) of thereceiver (1, 43, 44, 54) with the outer conduits for heat transfer fluidentrance.

64. Thermal insulation in the rear part of the receptacle (24).

65. Pressure gasket of the collector cylinders (73) and (74) of thetubes (19) of the receiver (1, 43, 44, 54), between the inlet and outletjunction.

66. Bent connection tubes connecting the inner tubes (19) of thereceiver (1, 43, 44, 54) with the outer conduits for heat transfer fluidexit.

67. Inlet conduit for conducting the heat transfer fluid to the receiver(1, 43, 44, 54).

68. Outlet conduit for conducting the heat transfer fluid from thereceiver (1, 43, 44, 54).

69. Shut-off and regulating valve for shutting-off and regulating thepassage of the fluid through the inlet conduit (67).

70. Shut-off and regulating valve for shutting-off and regulating thepassage of the fluid through the outlet conduit (68).

71. Gas extraction conduit for creating a vacuum in the receptacle (24).

72. Shut-off and closing valve for shutting-off and closing thevacuum-creating conduit (70).

73. Collector cylinder of the tubes (19) of the receiver at the inletjunction.

74. Collector cylinder of the tubes (19) of the receiver at the outletjunction.

75. Physical separation between the central bundle (20) and the adjacentbundle (21) which forms the thermal separation (41) in the case of FIG.9.

76. Physical separation between the central bundle (20) and the adjacentbundle (22) which forms the thermal separation (42) in the case of FIG.9.

77. Adjacent bundle similar to (21) in the case of an assembly withoblique bundles.

78. Adjacent bundle similar to (22) in the case of an assembly withoblique bundles.

79. Physical separation between the central bundle (20) and the adjacentbundle (77) forming the thermal separation (41) in the case of FIG. 4.

80. Physical separation between the central bundle (20) and the adjacentbundle (78) forming the thermal separation (42) in the case of FIG. 4.

81. Closest point of the mirror (5) closest to the receiver.

82. Furthest point of the mirror (5) furthest from the receiver.

The invention requires arranging a group of high pillars or columns (8)forming a longitudinal line like that shown in FIGS. 1 and 2, thereceiver (1) being supported in said line of pillars, usually in a dualversion, although in some assemblies, especially in the east-westdirection, a single receiver can be chosen, as in FIG. 2. The array oflongitudinal mirrors (7) supported on their solid turn axes (14), inturn supported by lines of low pillars (9) which intersect the latter inthe rotating junction parts (15), is arranged parallel to that line.Taking into account that the arrangement is uniform in the longitudinaldirection and can have the desired length, the description of theinvention and its quantitative details are in the corresponding workingplane, which is always normal to the longitudinal assembly axes, whichare parallel to one another.

The receiver (1) is an elongated, balanced expansion and pressure typereceptacle the active surface (2) of which is highly absorbent to solarradiation (4) and is struck by the radiation reflected (6) by eachmirror (7) of the array. The tubes (19) through which the heat transferfluid passes are grouped in at least three hydrodynamically independentbundles, a central bundle (20), which occupies the central half of theactive surface of the receiver (1) as a reference value, and two otheradjacent bundles on one side (21) and on the other side (22) of thecentral bundle (20), each occupying 25% of the active surface (2) as areference value. FIG. 3 depicts a cross-section of this arrangementbearing in mind that the receivers are positioned according to thatindicated in FIGS. 1 and 2.

There is a variant which allows using certain advantages in thecollection of radiation and in the effective separation of the bundles.To that end, and in line with the trapezoidal section of the receptacle(24), the bundles of longitudinal tubes (19) are arranged obliquely toone another, the central bundle occupying the central wall of the bottomof the receptacle, while the adjacent bundles are placed parallel with acertain rotation with respect to the central bundle, as schematicallyillustrated in FIG. 4. The group of bundles has a certain cavity shape,and the entire angle through which the radiation arrives is covered bythe active surface of the tubes. To that end, a covering is made withthe bundles which even creates a small area in which a shadow of the endof one bundle is cast on the contiguous bundle, with an extension nogreater than half the radius of the tube in the shadow, but enough so asto not lose radiation in the gaps which there must be between thebundles to prevent heat transfer from the central bundle to the adjacentbundles. With such an oblique covering, there furthermore is no physicalcontact between the ends of both bundles, thermal insulation partsfurther preventing the passage of convection currents being able to beinterposed between them without physical contact with both bundles atthe same time if there is filling gas in the receptacle (24) of thereceiver (1).

The receptacle (24) is built with a trapezoidal perpendicular section,its transparent outer window (28) having a greater width than the widthof the rear wall, the receptacle (24) having open side walls at the endof which there are located gaskets (31) in which the transparent window(28) is anchored, the bundles of tubes being maintained in theirpositions by the bent tubes (63) and (66) and their collector cylinders(73) and (74) traversing the receptacle (24) of the receiver (1) whichis suspended from the securing columns or pillars (8) through theattachment parts (16), (25).

The concentrated radiation (6) of the highest intensity (W/m²) willstrike the central bundle (20), and the two adjacent bundles (21, 77) onone side and (22, 78) on the other side collect radiation of lessintensity, since the intensity will be virtually nil on the outer edgeof their surfaces. FIG. 5 depicts, transversally on the active face (2),the profile of the intensity I (40) in W/m² striking said face, wherethere will be a portion of it (36) in which the striking intensity (40)is not nil, the surface (37) corresponding to the central bundle (20) inwhich the value of the intensity is markedly greater than in thesurfaces (38) and (39) corresponding to the adjacent bundles (21, 77)and (22, 78) which are physically separated from the central bundle (20)and thermally insulated from it through longitudinal insulations (23)which establish thermal separations (41) and (42) between the heatdeposited per unit of surface area in the central bundle (20) and theadjacent bundles (21) and (22), those thermal separations (41) and (42)being formed by means of parts (75) and (76) if adjacent receptacles areused to differentiate the bundles, and by means of parts (79) and (80)in the case of assemblies of oblique bundles, being distinguished.

Each receptacle (24) for the receiver (1) is made with measurementsaccording to the mechanical strength of the material used, thereceptacles (24) being successively arranged, which is used forabsorbing the expansions and contractions of the tubes (19) as a resultof their bent inlet connections (67) and bent outlet connections (68),as seen in FIG. 8, presented as illustrative complement, but without anyclaimed element relating to it directly. The fluid comes through thecollecting conduit (67) from the outlet of the preceding receptacle orfrom the delivery pipe from the thermal application and is distributedthrough the tubes (19) of the bundle in question by means of a collectorcylinder (73). FIG. 9, which is also presented as an illustrativecomplement and also having no claimed element relating directly to it,best shows this arrangement, the central bundle (20) with its specifictransparent window (60), separated from the adjacent bundles (21) and(22) with their respective windows (61) and (62) proposed as beingpointed or semicircular for a better mechanical resistance of the innervacuum, being distinguished. The bundles (20), (21), (22) are separatedby thermal separations (75) and (76) in which the windows (60), (61),(62) are inserted. Pressure gaskets (65) of the collector cylinders withhemispherical heads rotating slightly for absorbing the changes inlength of the tubes (19) and further supporting said tubes in position,are supported against said separations. A thermal insulation (64)encasing the outer connection tubes communicating one receptacle withthe next receptacle, or with the general outer circuit for connectionwith the thermal application must be arranged in the rear part of thereceptacle (24). Patent ES 2 321 576 82, which is the source of FIG. 9,includes no proposal in the specification or any mention in the claimsas to dividing the radiation absorbing tubes into bundles because of thehierarchy established between them depending on the level of radiationintensity received, or about the hydraulic path along which the heattransfer fluid runs through the various bundles. Dividing the tubes intoseveral bundles in said patent is due to reducing the mechanical stressof the glass windows of each bundle, reducing the width thereof.

Each mirror is made to follow the same rotation specification pattern toprovide the associated focusing on the Sun of the invention, and this isdone using the normal to the mirror (7) in its central point in theprojection of the mirror on the working plane as a tool. The mirror (7)rotates until this normal coincides with the bisector of the angleformed by the central ray of the solar beam striking the central pointof the mirror (7) and the line joining said central point of the mirrorwith the central point (3) of the active surface (2) of the receiver(1), all expressed in the projection in the optical or working plane.

The inclination of the active surface (2) of the receiver (1) is definedin terms of this surface being normal to the bisector of the field fromthe central point (3) of the active face (2) of the receiver (1), saidbisector being that of the angle which is formed with the lines goingfrom the central point (3) of the active face (2) of the receiver (1) tothe central point (34) of the mirror (5) closest to the receiver (1),and to the central point (35) of the furthest mirror (32). With respectto the height of the central point (3) of the active face (2) of thereceiver (1), it is advisable to limit the angle of vision of thecentral point of the receiver from the central point (35) of thefurthest mirror on the horizontal of the location to a value selectedbetween 10° and 80°, with an optimal value 45°, through elementalgeometric orientations.

As depicted in FIG. 6, in dual assemblies with two symmetrical receivers(43) and (44) with faces opposite one another, the fluid is circulatedthrough the adjacent bundles (46) of the first face, which is the onereceiving less radiation intensity, after having received the fluid fromthe pipelines (45) supplying it in relatively cold conditions from thethermal application, and after that first passage, they are directed bymeans of an outer connection (48) to the adjacent bundles (49) of thesecond receiver (44), thus ending the pre-heating phase in which thevalues in the peripheral areas (38, 39) of the radiation sent by thefield of mirrors (7) and striking the active face (2) of the receiverare used. The fluid from the adjacent bundles (49) of the secondreceiver (44) then enters the central bundle (47) of the first receiver(43) through an outer connection (50) where the levels of concentratedradiation are higher in intensity (37), this measurement being in wattsper unit of surface area, making the fluid acquire higher temperatures,and this greater heating is completed when the fluid passes through thecentral bundle (52) of the second receiver (44), which it reaches fromthe central bundle (47) of the first receiver (43), through anotherouter connection (51), and from which it exits through the outer duct(53) to go to the thermal application, as shown in FIG. 6. After thatquadruple run, the fluid has the high temperature which is necessary forobtaining a good thermodynamic performance.

For assemblies like that shown in FIG. 2 with a single receiver (1) orwith two receivers (54) geometrically parallel to but hydraulicallyinsulated from one another as shown in FIG. 7, the fluid enters theadjacent bundles (56) through the collection (55) of fluid from thesupply pipe coming from the thermal application, circulates in onedirection through the adjacent bundles (56) and, when reaching the endof that first passage, is injected by means of an outer connection (57)into the central bundle (58), where it is heated to a high temperatureand sent to the collection pipe (59) which carries it to thermalapplication.

Obviously the design of a power plant of this type will adjust thelength of the receivers to totalize the desired thermal power, but thismagnitude is not everything. The temperature reached, which is whatgives the heated heat transfer fluid a high exergy, is very important,and to that end the invention contains that division of the activesurface into at least the three aforementioned bundles. If the fluidwere to pass through all the tubes, mixing from time to time or almostcontinuously, the fluid of the central tubes would lose its temperaturewhen mixed with the low-temperature peripheral fluid, and the result ofthat mixture, as with that of any other, would be an increase in entropyand a loss of exergy. Hence the heating process is performed graduallyand hierarchically in this invention, achieving not only that the heattransfer fluid carries a considerable amount of thermal energy, but alsoat a high temperature, which is very useful for obtaining goodthermodynamic results.

Having clearly described the invention, it is hereby stated that theparticular embodiments described above are susceptible to modificationsin detail provided that they do not alter the fundamental principle andthe essence of the invention.

1. A receiver with longitudinal mirrors for a solar power plant, basedon a balanced expansion and pressure collector or receptacle receivingradiation from an array of concave mirrors parallel to one another,having a markedly longitudinal geometry with a greater length than widthwhich can rotate about a longitudinal axis of symmetry, which in turn isan axis serving as support in bearings, which are placed on at intervalspillars are buried in the ground and rigidly support the bearings,therefore the securing shaft, which is a rotating shaft, is always fixedin a straight line position, each mirror being orientated for reflectingradiation towards at least one longitudinal solar receiver, thelongitudinal axis of symmetry thereof located at a height above theheight of the axis of the mirror closest to the receiver as a result ofcolumns or pillars supporting the receiver, with an active facereceiving radiation reflected by the mirrors; said receiver having alongitudinal geometry and a greatest length parallel to the longitudinalaxes of the mirrors, and having an angle of inclination transverse tothe horizontal, there being a final mirror furthest from the receiver,two fields of mirrors being able to be assembled symmetrically withrespect to two parallel receivers with active faces arranged oppositeone another, each face pointing to a field, in assemblies in which thelongitudinal axes follow a local meridian, and being assembled both tothe north and to the south of the receiver in cases in which thelongitudinal axes of the mirrors are parallel to a local astronomicallatitude, in which assemblies can also be two parallel receivers withactive faces arranged opposite one another, each face pointing to afield, and in which positions and angles are expressed in a coordinatesystem in a working plane used, which is always normal to thelongitudinal assembly axes, which are parallel to one another; and ay-axis of the coordinate system in the working plane being a verticalline passing through a central or mid-point of the segment representingthe active face of the receiver in the working plane, and an x-axisbeing a horizontal line passing through the central point of the segmentwhich, in the working plane, represents the mirror closest to thereceiver, with a transverse width of the active surface or face of thereceiver selected from a value in the order of 1% of a straight linedistance between the central point of the furthest mirror of the fieldand the central point of the active surface of the receiver; selectingan angle of vision of the central point of the receiver from the centralpoint of the furthest mirror in a range of values between 10° and 80°,measured on the horizontal of the location; and the inclination of theactive face of the receiver being determined with the segment markingsaid surface in the working plane being perpendicular to a bisector ofthe field, said bisector being at an angle formed with the lines going,respectively, from the central point of the active face of the receiverto the central point of the mirror closest to the receiver, and to thecentral point of the furthest mirror; a group of controllable pumps andvalves being arranged which are external to the receiver but essentialfor the operation of the invention to force heat transfer fluid tofollow required movements through the hydraulic circuits of thereceiver; the solar radiation reflected by the different mirrors finallystriking a receiver inside of which there are arranged longitudinaltubes through which a heat transfer fluid feeding a thermal applicationcirculates; the active face of the receiver being the outer surface ofthe tubes where the radiation strikes, or the active face, where theradiation strikes, being thermally connected with the surface of thetubes, which are grouped in at least three separate bundles,transversally, there being a central bundle of longitudinal tubes, andat least two adjacent bundles and, one on each side of the centralbundle, the bundles being able to go in the same receptacle or inadjacent receptacles, but without mixing heat transfer fluid streamswhen passing through the receiver, the central bundle and adjacentbundles and having longitudinal thermal insulation between one anotherseparating the bundles; and the percentage distribution of the totalactive surface of the receiver between the central bundle of tubes andthe adjacent bundles and being a value selected from the central bundleoccupying 99% of the active surface, and the adjacent bundles andoccupying the rest; and the central bundle occupying 20%, the adjacentbundles and occupying the rest; giving 50% of the active surfaceoccupied by the central bundle as a distribution reference value and theadjacent bundles (21) and each occupying 25% of the total active surfaceof the receiver on either side, wherein the bundles of longitudinaltubes of the receiver are arranged obliquely to one another, the anglethrough which the radiation arrives being covered by the active surfaceof the tubes as a result of the covering provided by the bundles, therebeing a small area in which a shadow of the end of one bundle is cast ona contiguous bundle, with an extension no greater than half the radiusof the tube in the shadow, without physical contact between the ends ofboth bundles, and thermal insulation parts further preventing passage ofconvection currents being able to be interposed between them withoutphysical contact with both at the same time if there is filling gas inthe receptacle of the receiver.
 2. The receiver with longitudinalmirrors for a solar power plant according to claim 1, wherein inassemblies with two symmetrical receivers and with faces opposite oneanother, the fluid is received from the pipelines supplying the receiverfrom thermal application and is circulated through the adjacent bundlesof the first face, which is the face receiving less radiation intensity;and after that first passage the fluid passes to the adjacent bundles ofthe other receiver by an outer connection, through which bundles, thefluid circulates thus ending a pre-heating phase in which values ofperipheral areas of the radiation sent by the field of mirrors andstriking the active face of the receiver are harnessed; the fluid fromthe adjacent bundles of the second receiver then entering into thecentral bundle of the first receiver through an outer connection, wherelevels of concentrated radiation are higher in intensity, being measuredin watts per unit of surface area, making the fluid acquire highertemperatures as the fluid passes through said bundle, and greaterheating is completed when the fluid passes through the central bundle ofthe second receiver, which the fluid reaches from the central bundle ofthe first receiver, through another outer connection, and from which thefluid exits through the outer duct to go to an thermal application.